This invention relates to bitter-tasting substances embedded in a substrate, by which means said substrate is provided a measure of protection against gnawing damage; and particularly to denatonium benzoate (Bitrex(trademark)) embedded in a polymer matrix.
Gnawing damage to plastic cable housing caused by rodents is a multimillion dollar problem; squirrels gnawing on exposed plastic cables cause multiple power outages around the country, while prairie dogs wreak havoc on buried cable in many parts of the Mid West. Heretofore, the Prior Art has attempted to prevent such gnawing damage by creating microcapsules filled with a capsaicine compound within a resin molding composition (Kurata, et. al., U.S. Pat. No. 5,456, 916). This entails the use of an insoluble dispersing medium (usually water); often an acid binding agent is also needed. However, creating microcapsules ensures that, the active agent will not be evenly distributed throughout the substrate. In particular, a solution or suspension of capsaicine in a resin matrix will not be created. There are disadvantages to forming microcapsules. Bubbles and inclusions are well known to cause stress concentrations which weaken the material in which they occur; microcapsules would similarly be expected to weaken the treated resins. The method disclosed for creating microcapsules would appear to require substantial modifications to current manufacturing apparatus; this is a substantial drawback. Further, the size of the microcapsules places a limit on how thin a sheet of resin or plastic can be manufactured, and the solvent could prove to be a painful eye irritant in the event of leakage. The creation of microcapsules is not necessary if the aversive agent is intense enough: a compound such as Bitrex(trademark) (denatonium benzoate), the bitterest substance known, is powerful enough to repel rodents without the need to resort to the xe2x80x9cstrength in numbersxe2x80x9d approach afforded by microcapsules. Embedding microcapsules in a resin matrix is an interesting approach, but has many drawbacks which are avoided by the present invention.
Harding (U.S. Pat. No. 4,795,637) discloses how to make a rodent-repellent powder. This powder offends the rodent""s sense of smell rather than its sense of taste; additionally the scent is not directly mixed into a specific substrate which is to be protected, but instead is applied to a general area.
An Internet entry (http://www.waite.adelaide.edu.au/xcx9cpclarke/science/bitter_the_most) of Nov. 23, 1996 alludes to denatonium benzoate (Bitrex(trademark)) being added to nail-polish, which is then painted on the fingernails of young children to prevent them from chewing their fingernails. Although this application might seem to superficially resemble the present invention, it in no way anticipates it. The present invention seeks to directly imbue a substrate with sensorially-active properties (for instance, the addition of Bitrex(trademark) to plastic cable sheathing to prevent rodents from chewing on the sheath). Bitrex(trademark) is not added to nail-polish to protect the nail-polish. Instead, the Bitrex(trademark) in the nail-polish protects whatever the polish is painted upon.
This difference becomes clear when viewed from the perspective of protected substrates. In the cable sheathing example, the substrate to be protected is the plastic sheathing itself. In the nail-polish example the substrate to be protected is the fingernail, but the Bitrex(trademark) has not been added directly to the fingernail. Instead, it has been added to nail polish, which is then painted over the fingernail. The equivalent in the cable sheathing example would be to spray a bitter-tasting compound onto the exterior of the cable sheath, rather than impregnating the plastic itself with this bitter-tasting compound.
The required physical properties of the substrates also differ. A xe2x80x9cnail-polish-typexe2x80x9d substrate must be either liquid or have adhesive qualities, or both. In contrast, a cable sheath cannot be liquid; nor should it possess adhesive qualities. It must provide structural integrity, precluding it from being a liquid; and must be easy to work with, precluding it from being sticky. Polymers like polyvinyl chloride and polyethylene, while excellent candidates for cable sheath substrates, would not be suitable materials for xe2x80x9cnail-polish-typexe2x80x9d substrates.
The present invention will not, in all likelihood, produce skin or eye irritation. Studies have shown Bitrex(trademark) to be non-irritating to the skin even in fairly high concentrations. If skin irritation were to become an issue, the sheath can be co-extruded with the Bitrex(trademark)-treated plastic contained inside of a normal plastic outer skin. Co-extrusion, while expensive, will greatly mitigate, if not completely eliminate, any objectionable side effects. Thorough rinsing should eliminate any residual traces of bitter substance which might be picked up on the hands and transferred to the mouth of a person handling plastic treated with Bitrex(trademark); handling treated plastic should not cause unpleasant bitter tastes in the mouths of the handlers.
Accordingly, besides the rodent-repelling objects and advantages described above, several objects and advantages of the present invention are:
Lamp cords made of Bitrex(trademark)-treated plastic which dissuade pets and young children from chewing on them
Thin sheets of Bitrex(trademark)-treated plastic which can be wrapped around furniture legs to minimize gnawing damage due to pets
Slipper soles made of Bitrex(trademark)-treated plastic which discourage gnawing by pets
Electric cable sheaths made of Bitrex(trademark)-treated plastic which deter rodents from gnawing on the cable sheaths
Optic fiber cable sheaths made of Bitrex(trademark)-treated plastic which deter rodents from gnawing on the cable sheaths
Environmentally-friendly rodent damage control
Energy savings, cost savings, and time savings due to greater cable longevity and the consequently reduced need to excavate and repair buried cables
Greater system reliability due to reduced rodent damage to system components
Coatings for above-ground power and telephone lines which protect against gnawing damage
Sheathing which can be wrapped around tree trunks to afford a measure of protection against beavers
Plastic exterminator suits which discourage rodent bites
Note that the substrate need not be plastic; it could be fiberglass or styrofoam or any material which can effectively retain the flavoring agent. Protection is not restricted to guarding against rodent gnawing damage; any animal which is averse to bitterness can be deterred from chewing on the treated substrate. The bitter agent is not restricted to Bitrex(trademark); other bitter substances such as quassin or sucrose octa-acetate could be used instead. Since Bitrex(trademark) readily dissolves in polyvinyl chloride, it can, in all likelihood, be added in the same step in which color is addedxe2x80x94or even added in lieu of color. This has the obvious advantage of not requiring a change to the production line or manufacturing processxe2x80x94keeping down production costs and allowing inexpensive trial batches to be made.